Adam Gilmore* and Lyufei Chen
*HORIBA Instruments Inc, 9 E View Ct, Flemington, NJ, 08822-4607
(adam.gilmore@horiba.com)

Commercial additive concentrates (CAC) derived from grapes with intensely colored skins and flesh (teinturier grapes) has become more commonplace, primarily to enhance color in finished wines. The target concentration is usually ≤0.2% by volume. Rarely is the use of CAC disclosed or discussed by the manufacturer, owing to a perceived stigma concerning the quality of the primary grapes used for winemaking. Malvidin-3,5-diglucoside is used as a specific chemical marker associated with CAC because it occurs naturally at much lower concentrations in the Vitis vinfera sp. grapes used for winemaking. The patented A-TEEM method acquires complete optical fingerprints in under one minute and facilitates linear calibration using the on-the-fly inner-filter effect correction of absorbance distortion. For wine, all A-TEEM measurements are collected under Beer-Lambert linear absorbance conditions at a constant temperature (20°C) using a standard solvent (50% EtOH, pH 2) and filtration protocol (0.45 mM pore size). The A-TEEM accurately quantifies most major anthocyanin compounds (including malvidin, cyanidin, peonidin, and petunidin), their most common monoglucosides, and their acylated and coumyralted forms from V. vinfera varieties, based on their unique optical properties for absorbance extinction and spectra, their fluorescence yields, and excitation and emission spectra. Anthocyanin quantification with A-TEEM is independent of grape variety and growth region and conditions. We validated that detection limits of CAC in wines, derived from partial least squares and extreme gradient boost regression methods from several V. vinifera varieties, are <0.03% v:v. We will report on our test results for validation of a variety-independent model. We conclude the A-TEEM method can be an effective tool to quantify CAC, which can be important for winemaking formulation and quality evaluation, including competitive products.

Funding Support: N/A